Deuteration of Water Enables Self‐Organization of Phospholipid‐Based Reverse Micelles

Abstract

Phospholipid-based reverse micelles are composed of branched cylinders. Their branching points are known to attract themselves and to slide along branches. The rate of this sliding is governed by the lifetime of H(D)-bonded water bridges between phospholipid molecules. This lifetime is increased when the water is deuterated. On condition that the water contains at least 40 D atoms%, water/dipalmitoylphosphatidylcholine (DPPC)/deuterated pyridine reverse micelles with the composition 1.1:1:250 (v/v) have been shown to self-organize into a liquid crystal in the 310-316 K temperature range. The mechanism of this self-organization is unraveled by following the FTIR and (1)H NMR spectra of more concentrated micelles upon heating. During the preparation of micelles, pyridine-(D(+))H(+) ions are formed. They give rise to hydron transfers, under the influence of the DPPC electric charges, evidenced by two broad FTIR absorptions above (BB1) and below (BB2) the nu(C-O) stretch. These hydron transfers occur along strong (D(+))H(+) bonds of pyridinium ions with pyridine (BB1) and DPPC C=O groups (BB2). The proton transfers at the interface of micelles, relayed in the continuous pyridine medium, create a tenuous link between separated micelles, thus facilitating their organization. Upon heating, DPPC heads shrink and DPPC chains expand to make wedge-shaped DPPC molecules. The micelles then change in shape: cylinders constrict and enclosed water drifts towards branching points, which swell. Branching points of neighboring micelles come into contact. Due to the deuteration of water these contacts are prolonged and H bonds are formed between DPPC molecules located in each branching point. Upon storage at 39 degrees C, these branching points fuse. The lateral diffusion of DPPC molecules becomes free, as evidenced by a narrowing of all (1)H NMR resonances. Upon further heating, reorganization into a liquid crystal occurs.

Excited-State Dynamics of an Environment-Sensitive Push–Pull Diketopyrrolopyrrole: Major Differences between the Bulk Solution Phase and the Dodecane/Water Interface

“…The first two effects should contribute to the substantial slowing down of the dynamics upon deuteration. Deuterium bonds are known to be stronger than hydrogen bonds, and thus the competition between interfacial water–water and water–DPP1 bonds should be further in disfavor of the latter in D 2 O. , Of course, isotopic substitution has a major impact on the vibrational modes of water and on their coupling with those of DPP1.…”

Ultrafast Energy Migration Pathways in Self-Assembled Phospholipids Interacting with Confined Water

“…Significantly less is known about reverse micelles formed from phospholipids compared to the ones formed from AOT. Several groups report the formation of isolated water droplets stabilized by lecithin, a mixture of naturally occurring phosphatidylcholines, in alkanes, − haloalkanes, and benzene. ,− In alkane solvents, lecithin tends to form a gel phase with added water. − In contrast, droplets remain isolated when reverse micelles form in benzene. ,− Although no reports of DOPC reverse micelles have appeared, DOPC forms a significant component of the naturally occurring lecithin phospholipid so we expect strong similarities between DOPC and lecithin reverse micelles. As it has frequently been used in studies of vesicles − or multibilayer films − as models of membranes or bilayers, employing DOPC facilitates direct comparison of our results to these systems.…”

NH3 Sensing Mechanism Investigation of CuBr: Different Complex Interactions of the Cu+ Ion with NH3 and O2 Molecules

“…However, the NH 3 gas sensing mechanism of CuBr remained unclear because of the its inherent characteristic of mixed ionic−electronic conducting. Diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) was a increasingly popular technique in catalysis research, and the formation of surface species study for it permitted in situ observation of the reaction in powder or granular form. − Therefore, the investigation of the NH 3 sensing mechanism of CuBr could be carried out through in situ DRIFTS.…”